A variety of medical devices exist for monitoring patient cardiac activity. For example, these devices may be implantable, subcutaneous, or adherent and may include one or more leads for monitoring electrical signals, e.g., intrinsic depolarizations of the hearts. Methods are used to extrapolate from the monitored electrical signals various cardiac events such as P-waves, R-waves and T-waves (referred to generically as sensed events). Based on these sensed events, cardiac episodes/conditions can be detected. For example, both bradycardia and asystole episodes are characterized by long pauses between sensed events (e.g., R-waves that signal a ventricular depolarization/contraction). However, a determination that a patient is experiencing a bradycardia or asystole episode is based on the assumption that all events have been properly sensed by the medical device. If the medical device under-senses one or more events within the episode, the medical device may incorrectly determine that the patient is experiencing a bradycardia/asystole type event.
In particular, the primary cause for inappropriate bradycardia/asystole detection is due to frequent premature ventricular contractions (PVCs) characterized by a wide QRS complex, PVCs characterized by a very large QRS amplitude, and small/wide QRS complexes. In the case of PVCs characterized by a wide QRS complex, the low-frequency characteristic of the QRS complex results in the PVC being under-sensed. In the case of PVCs characterized by a very large QRS amplitude, the amplitude of the PVC beat results in the under-sensing of normal QRS amplitudes that following the PVC beat. In both cases, the result of under-sensing events results in an inappropriate detection of a bradycardia/asystole event.
It would therefore be desirable to minimize the inappropriate detection of bradycardia/asystole episodes.